[47] The basin of Nero was possibly cut through the layer of tufa, which underlies the whole soil of Rome, down to the clay under it. In some excavations made under my direction in a cave under the Aventine, near the Marmorata, which was the mouth of the Aqua Appia, a level bed of white clay was found under the tufa rock of which the Aventine Hill consists; this would account for the walls in the central part built of concrete and brick, on this clay foundation, having been frequently damaged by earthquakes, while the great stone arcades, being built upon the tufa rock, did not suffer from the shocks. Clay is always a bad foundation to build upon, and there are always settlements in buildings that rest upon it. The objection to this theory is, that the surface of the water would be twenty-one feet below the arena and the foot of the _podium_. [48] See Plate IX. [49] In the ancient catalogue of the Emperors and their works, known as “Catalogus Viennensis Imp. Rom. apud Eccard.,” under Vespasian, it is stated that he dedicated the first three steps of the amphitheatre, implying that three were already finished even in his time. [A.D. 70.] “Hic prior tribus gradibus amphitheatrum dedicavit;” That Titus added two more. [A.D. 81.] “Hic amphitheatrum a tribus gradibus patris sui dura adjecit.” And further, that Domitian completed the building up to the clypea, that is, the top cornice at that time, when the upper storey was of wood. [A.D. 92-96.] “Domitianus Imp. ... Amphitheatrum usque ad clypea.” [50] See Plates V., VI., XV., XVI. [51] Photos., Nos. 3136, 3137. [52] Photos., No. 3204. [53] This platform was, perhaps, constructed of a great number of timbers fastened together. Lucan has described such a platform with a tower on it. (Pharsal., lib. iv. 420, sqq.) [54] Dionis Hist., lib. lxii. cap. 15. [55] Ibid., lib. lxi. Nero, vi. c. 9 and 17. [56] Ibid., lib. lxvi. c. 25. [57] Ibid., lib. lxii. Nero, iii. c. 15, and 20, 22. [58] “Spectacula magnifica assidue et sumptuosa edidit, non in amphitheatro _modo_, rerum et in circo ... ac in amphitheatro, navale quoque.” (Suetonii Domitianus, c. 4.) [59] Dionis Hist., lib. lxii. c. 18. [60] “Omnis Cæsareo cedat labor Amphitheatro: Unum pro cunctis fama loquatur opus....” (Martialis, De Spectaculis, Epigr. 1.) “Hic, ubi conspicui venerabilis Amphitheatri Erigitur moles, stagna Neronis erant.” (Ibid., Epigr. 2.) [61] Taciti Ann., xv. 42. [62] Ibid., lib. xiv. c. 15. [63] Ibid., c. 31. [64] “... lacu in ipso navale prælium adornatur, ut quondam Augustus, structo cis Tiberim stagno; sed levibus navigiis et minori copiâ ediderat.” (Taciti Annal., xii. 56.) [65] “Igitur in stagno Agrippæ (Tigellinus) fabricatus est ratem, cui superpositum convivium aliarum tractu navium moveretur ... volucres et feras diversis e terris, et animalia maris Oceano abusque petiverat.” (Taciti Annal., lib. xv. c. 37.)